1. Field of the Invention
The present invention relates to an optical sensor that emits light and detects the reflected light to determine if there is a target object in front of the sensor.
2. Description of the Related Art
Certain optical sensors that detect whether or not there is a human body or hand in front of an electronic device are known.
In an optical sensor described in Japanese Unexamined Patent Application Publication No. 2001-194232, a light emitting portion and a light receiving portion are arranged side by side on a substrate and a transparent board is disposed in front of the light emitting portion and the light receiving portion. When infrared rays emitted from the light emitting portion pass through the transparent board to the front and are reflected off a target object in front of the transparent board, the reflected light is received by the light receiving portion. By monitoring the amount of light received by the light receiving portion, it is determined whether or not there is a target object in front of the sensor.
In the optical sensor described in Japanese Unexamined Patent Application Publication No. 2001-194232, the light receiving portion receives not only the light reflected off the target object but natural light such as sunlight. Thus, when strong natural light is supplied to the sensor of an electronic device, the accuracy with which the sensor detects a target object decreases.
In view of the circumstances, the following configuration is conceived of in order to compensate for the decrease in detection accuracy due to the natural light. Specifically, in the configuration, a light-guiding member made of a light-transmissive material is disposed in front of the light emitting portion and the light receiving portion so as to guide some infrared rays emitted forward from a detection-light-emitting portion, so that those rays are received by the light receiving portion. Further, the light-guiding member guides infrared rays emitted from a monitor-light-emitting device to cause the light receiving portion to receive the light. The amount of light received by the light receiving portion after being emitted from the detection-light-emitting portion and the amount of light received by the light receiving portion after being emitted from the monitor-light-emitting device are compared to each other so that the decrease in detection accuracy is compensated for.
The optical sensor having the above configuration, however, needs to be adjusted such that the amount of light received by the light receiving portion after being emitted from the detection-light-emitting portion is balanced with the amount of light received by the light receiving portion after being emitted from the monitor-light-emitting device. Such an optical sensor is difficult to design. Particularly, if the optical sensor includes multiple detection-light-emitting portions, balancing of the amounts of received light becomes more difficult.